[Bug lto/54933] New: 'builtin symbol' referenced in section ... defined in discarded section

[Bug lto/54933] New: 'builtin symbol' referenced in section ... defined in discarded section

[chrbr at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54933

             Bug #: 54933
           Summary: 'builtin symbol' referenced in section ... defined in
                    discarded section
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: chrbr@gcc.gnu.org
            Target: x86


Created attachment 28450
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28450
preprocessed files

The attached case is a self-content skeleton reducing a newlib build, that
builds with -fno-builtin, used in a standard way (e.g no -fno-builtin.

this illustrates a problem when "malloc" and "free" are defined from the same
file, but the prevailing "free" version is called from no-builtin site, and the
"malloc" builtin version is called from the main site, so we get:

---
`malloc' referenced in section `.text' of bug.ltrans0.ltrans.o: defined in
discarded section `.text' of malloc.o (symbol from plugin)
---

malloc is PREVAILING_DEF_IRONLY. shouldn't it be PREVAILING_DEF ?

tested with binutils 2.22 and 2.23.51

[Bug lto/54933] 'builtin symbol' referenced in section ... defined in discarded section

[joey.ye at arm dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54933

Joey Ye <joey.ye at arm dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |joey.ye at arm dot com

--- Comment #1 from Joey Ye <joey.ye at arm dot com> 2013-01-18 06:33:20 UTC ---
This issue especially impacts "retarget", where library functions are
"retargeted" to user implementations. Retarget is a common practice in
bare-metal development but runs into "defined in discarded section" with LTO
enabled.

Here is the retarget case:

# gcc version 4.8.0 20130115 (experimental) [trunk revision 195189] (GCC)
# GNU ld (GNU Binutils) 2.23.51.20130111
$ cat main.c
int main()
{
    return puts("Hello");
}

// it works if following line is enabled
// __attribute__ ((used))
int _write(int c)
{ 
    /* Do something */
    return c; 
}
$ cat lib-a.c 
int puts(const char * str)
{
    return _write(*str);
}
$ gcc -flto   -c -o lib-a.o lib-a.c
$ ar rv liba.a lib-a.o
r - lib-a.o
$ gcc main.c liba.a -flto --entry=main -nostdlib -o l
`_write' referenced in section `.text' of liba.a(lib-a.o): defined in discarded
section `.text' of /tmp/ccwUUKiA.o (symbol from plugin)
collect2: error: ld returned 1 exit status